The present invention relates chiefly to obstacle detecting apparatus and method for detecting an obstacle present on the road, such as a vehicle running ahead, a parked vehicle, and a pedestrian, through the use of a camera mounted on the vehicle, in order to assist safe driving and achieve automatic driving of the vehicle.
There are known two methods employed to detect an obstacle present on the road: one uses an active sensor, such as a laser range finder, an ultrasonic sonar, and a millimeter wave radar, and the other uses a passive sensor, such as a visible-light CCD camera and an infrared camera.
The active sensor is used to determine the position of a given object for various purposes, and its usefulness has been widely known. However, when used for the purpose of detecting an object causing obstruction to driving of the vehicle, such as another vehicle on the road, the active sensor has problems as follows: it has low detection resolution; it cannot cover a sufficient measuring range; it erroneously detects an object on the road other than an obstacle; and, because of the inability to detect each driveway lane, it erroneously detects an object along the roadside that would cause no obstruction. Thus, in order to solve these problems, there has been a need for a sophisticated obstacle detecting technique through image analysis using a passive sensor, such as a CCD camera.
Broadly speaking, the method of detecting an obstacle through analysis of an image sent from a CCD camera or the like mounted on the vehicle may be deemed as a method of detecting an obstacle or recognizing the driving lane from luminance pattern information of the image. The driveway lane may be detected through the use of an image sent from a single camera by extracting a gray portion where the texture is less dense.
In practice, however, many obstacles have luminance or patterns similar to those of the road, which makes it difficult to achieve a highly practical obstacle detecting apparatus capable of operating with less erroneous detection.
On the contrary, a method, generally referred to as the stereo vision, using a plurality of cameras has been employed to detect an obstacle and the driveway lane.
According to the stereoscopic-view method, three-dimensional information within a detection target range can be obtained, and achievement of highly accurate obstacle detection or lane detection is expected. However, a problem of this method is that, in general, a correspondence search to find a single point in the real world appearing in a plurality of camera images cannot be performed in a univocal manner. In this regard, methods disclosed in JP-2001-76128A and JP-2000-293693A (Japanese unexamined patent publications No. 2001-76128 and 2000-293693) eliminate the need of the correspondence search, and therefore, are quite advantageous in achieving the lane detection and the like.
However, in a case where there is parallax in the guardrail along the roadside, or in the texture like the white line or signs on the road surface due to the slope or change in the pitching angle of the vehicle, there arises a problem that the guardrail and the texture on the road surface, neither of which causes obstruction to driving of the vehicle, is detected erroneously as an obstacle. Also, in the case of rainy weather, there is a problem that raindrops adhering to the windshield or the lens surface of the camera are erroneously detected as an obstacle.